The information provided below is not admitted to be prior art to the present invention, but is provided solely to assist the understanding of the reader. All U.S. patents and patent applications and other published documents mentioned anywhere in this application are incorporated by reference in their entirety.
The family of semi-automatic firearms based on the original ARM ELITE AR-15 and COLT M16 rifles has achieved significant success with military, law enforcement and civilian shooters alike and is currently one of the broadest and most popular in the world. Improvements to the AR-15/M16 platform are diverse in their purpose, with new embodiments and aftermarket parts and accessories continually being developed due to the overwhelming popularity and inherent modularity of the base platform. Although the template firearm design itself has undergone many refinements to improve its functional reliability, to expand its mission roles, and to reduce its manufacturing costs, the design's principles of operation have not been significantly improved. In fact, firearms patterned after the reputable AR-15/M16 template using the same basic design features and specifications are currently produced in numerous calibers and countless versions and configurations by different manufacturers throughout the world.
The term “AR-15®” as used herein refers to the rifle manufactured by COLT DEFENSE LLC or its licensees at the time of invention. Semi-automatic variants and derivatives of the AR-15/M16 produced by other manufacturers are usually termed “AR-15 type” or “AR-15 style” regardless of caliber and are sold under various proprietary model designations. The term “AR type” is used in this disclosure to refer to authentic semi-automatic COLT firearms based on the AR-15/M16 platform such as the AR-15, AR-15 Sporter SP1, AR-15A2 Match Target and AR6720, as well as semi-automatic versions of AR-15 type firearms such as the ARMALITE AR-10, REMINGTON R-15 and the BUSHMASTER XM-15 rifles at the time of invention.
The use of lighter weight synthetic materials such as reinforced composites and polymers (collectively, “polymers” or “synthetics”) to form various parts of a firearm such as a receiver or frame for a handgun or rifle has increased significantly in recent years. Lighter weight synthetic materials provide the firearm with a reduced weight for ease of carrying, handling and use in the field, on the range and during combat. For example, by reducing the weight of a firearm, the user generally is able to manipulate the firearm faster and easier, such as while tracking moving targets. The lighter weight also means less load that must be borne by the user during transport and use, which conserves the user's energy, reduces fatigue and increases accuracy. Additionally, most lighter weight synthetic materials now being used for firearms are typically less susceptible to corrosion and damage resulting from exposure to water, salt, dirt, and other environmental hazards. Moreover, many modern polymers are easier and less costly to manufacture into firearm components than traditional metal substrates such as forged aluminum, aluminum billet or steel, making components formed from synthetic materials more affordable.
A major problem associated with the use of lighter weight polymer materials to form parts of a firearm, particularly receivers and actions, is that such materials sacrifice strength and the ability to withstand the extreme pressures and stresses created upon firing a round of ammunition in exchange for lighter weight. For example, upon discharge of an AR type firearm, the basic design of which is well known in the art, the bolt is forced rearward to an open position to eject the spent cartridge and ready the chamber to receive a new round, after which the new round is loaded in the chamber by the capture and backflow of gases created upon the firing of the previous round of ammunition. The extreme chamber pressures and recoil forces resulting from the travel of the bolt are primarily borne by the receiver of the firearm. Over time, such extreme stresses can cause cracking and potentially failure in a receiver formed from some lighter weight synthetic materials. For example, the primary point of stress and the most likely point of failure in an all polymer lower receiver for an AR type firearm is around the threaded ring or collar disposed at the rear end of the lower receiver body that is configured to accept and connectively engage with a threaded receiver extension (also commonly and interchangeably known as a “buffer tube”). Much of the stress caused by the recoil force of a discharging AR type firearm is focused around the point where these two components engage.
A further related consequence of using lighter weight, polymer-based materials such as plastics and reinforced composites to form synthetic firearm receiver bodies has been that such materials typically are not as durable as conventional forged steel or aluminum, the traditionally preferred substrates for firearm receivers. More pointedly, the threaded portions of all-polymer receivers tend to wear out more quickly, especially when connectively engaged by conventional metal screws or screw threads, which leads to a higher chance of failure and thus an increased risk of firearm malfunction and shooter injury during use. This defect is of particular concern to users of AR type polymer lower receiver bodies (as used herein, the term “lower receiver body” means a lower receiver stripped of all its operational components, also commonly known in the art as a “stripped” lower receiver) because many of the currently available parts, components and accessories for AR type firearms, such as the buffer tube and pistol grip retaining screw, are still made from one or more types of metal and are configured to engage the lower receiver body using screw threads. No suitably strong, yet lightweight AR type stripped lower receiver durable enough to lastingly withstand recoil stress and engagement with metal screws is currently available.
More durable, lighter weight AR type stripped receivers, including upper and lower receivers and lower receiver assembly kits are still being sought. As a result, it is desirable to provide a threaded metal insert for a polymer lower receiver body, particularly for an AR type polymer lower receiver such as that of an AR-15 or AR-10, that provides the greater durability and increased strength and longevity of traditional metal alloys but which does not substantially affect the lighter weight imparted by the polymer. It is also desirable to provide an inexpensive, hybrid polymer and metal stripped lower receiver for an AR type firearm such as an AR-15 or AR-10 that overcomes the foregoing shortcomings of the prior art to deliver a lighter weight, corrosion resistant, stripped lower receiver having superior strength and durability that functions with substantially all high quality conventional AR type (upper and lower) receiver parts kits, yet does not require the use of any specific caliber, brand or type of parts. It is also desirable to provide methods for economically manufacturing such threaded metal inserts and hybrid polymer lower receivers. Accordingly, a need exists for an improved polymer lower receiver for AR type firearms that addresses the foregoing and other related problems in the art to combine the lighter weight and corrosion resistance of all-polymer lowers with the greater strength and durability of traditional metal components. Other objects and advantages will become apparent from the following disclosure.